//自定义选择器
function st(select){
    select = select.trim();
    let first = select[0];
    let two = select.slice(1,select.length);
    switch(first){
        case "."://选择class名
            return document.getElementsByClassName(two);
            break;
        case "#"://选择id名
            return document.getElementById(two);
            break;
        case "@"://选择name名
            return document.getElementsByName(two);
            break;
        default:
            return document.getElementsByTagName(select);
    }
}
